Many manufacturing and processing methods generate effluents which, on the one hand, cannot be directly disposed of via the sewers because of their composition and, on the other hand, contain substances the recovery and reuse of which would be economically gainful. One example is the photographic processing industry, in which exposed silver halide photographic films and papers are treated in successive processing baths that are rich in chemicals. Such photographic film processing methods are well known (see for example, Chimie et Physique Photographiques; Pierre Glafkides, Vol. 2, Chap XL, pages 947-967).
In general photographic processing comprises several processing baths and one or more wash and/or stabilization baths. The build-up in the wash and/or stabilization baths of substances carried over from the preceding processing steps is especially detrimental not only to the stability of developed photographic images and to the good keeping of sensitometric characteristics, but also to the possibility of recycling these wash and stabilization baths, or discharging them to the sewers. After processing, the wash and stabilization baths are found to contain inorganic compounds, such as iron, silver, thiosulfate, and sulfate ions, or organic compounds which are, either substances used for development, or products coming from the reaction of these substances during development, or from the step of fixing or bleach-fixing.
The problem of discharging silver to the sewers is especially important because of new standards that apply to photographic processing methods. There are notably standards that set the maximum volume of water that should be used for washing 1 m.sup.2 of photographic material. In particular, for processing X-radiographs, the current French standard permits the use of 15 liters of water per m.sup.2 of single-coated radiographic product to be processed and 30 liters of water per m.sup.2 of double-coated radiographic product, with discharge to the sewers of water containing a maximum of 1 ppm of silver. Reducing the permissible volume of water produces wash baths that are more concentrated in silver and thus more difficult to decontaminate. Therefore it is necessary to have a processing method that is both efficient and complies with the standards. It is also useful to have a method that is easy to apply and economic.